1. Field of the Invention
The invention relates to a metallic substrate, and more particularly to a fabricating process and a structure of a thermal enhanced substrate for being used by light emitting devices.
2. Description of Related Art
A Light Emitting Diode (LED) is a light emitting device mainly comprising III-V or II-IV group compound semiconductors. In comparison with the disadvantages of conventional bulbs, which are high electricity consumption, high heat radiation and poor shock resistance, because the operating principles and the structures of light emitting diodes are different from those of conventional bulbs, the light emitting diodes have numerous advantages including miniature sizes, durability, low-driven voltages, fast response speed and good shock resistance, and therefore they are widely applied to various fields of electronic products including portable communication products, traffic signs, outdoor display panels, illumination for vehicles and illuminators.
Nevertheless, along with the development of the fabricating techniques, the emitting efficiency of the light emitting diodes is gradually increased, so the emitting brightness can be advanced further more, thereby meeting and expanding the requirements for all kinds of illuminating products. In other words, in order to increase the brightness of the light emitting diodes, in addition to solving the outer package problems of the light emitting diodes, there is a need to design the light emitting diode with a higher power and a higher working current, in hope of fabricating the light emitting diode having high brightness. However, under the circumstance of increasing the power and the working current, the light emitting diodes will generate relatively more heat, so the performance thereof is easy to be compromised by overheat and in a serious situation, it even causes the malfunction of the light emitting diodes.
FIG. 1 is a schematic view of a conventional metallic substrate electrically connected with a light emitting diode by using a PTH (plated through hole). As shown in FIG. 1, a light emitting diode 100 is disposed on a thermal conduction block 112 of a metallic substrate 110, and an electrode of the light emitting diode 100 is electrically connected with a PTH (plated through hole) 114 of the metallic substrate 110 through a conductive wire 120, so as to drive the light emitting diode 100 to illuminate by a working current. In addition, most heat generated by the light emitting diode 100 can be dissipated through the conduction of the thermal conduction block 112, thereby preventing the working temperature of the light emitting diode 100 from being overly high.
Moreover, a small part of heat generated by the light emitting diode 100 is conducted to the PTH 114 through the conductive wire 120 and is then dissipated through conduction by the PTH 114. Because the volume of the PTH 114 is far smaller than that of the thermal conduction block 112, the PTH 114 does not help much in lowering the working temperature of the light emitting diode 100. Therefore, most heat has to be dissipated through the thermal conduction block 112 under the light emitting diode 100, and consequently the conventional metallic substrate 110 cannot provide a larger heat dissipation area. Besides, because the miniature PTH 114 is fabricated by performing a micro-fabricating process on the metallic substrate 110, the difficulty of the fabricating process is increased, thereby causing an increase of the cost in the fabricating process.